Looks like a 1:3 twist??Hmmm … 8.6 is roughly a .338. A 300gr subsonic .338 round better be spinning pretty damn fast or it’s gonna become unstable and be tumbling real quick … a 1:7 twist ain’t gonna get it.
Looks like a 1:3 twist??
https://www.arbuildjunkie.com/8-6-blackout-a-2021-update-with-qs-kevin-brittingham/